ASoC: tas2770: Fix handling of mute/unmute

Because the PWR_CTRL field is modeled as the power state of the DAC
widget, and at the same time it is used to implement mute/unmute, we
need some additional book-keeping to have the right end result no matter
the sequence of calls. Without this fix, one can mute an ongoing stream
by toggling a speaker pin control.

Fixes: 1a476abc

 ("tas2770: add tas2770 smart PA kernel driver")
Signed-off-by: Martin Povišer <povik+lin@cutebit.org>
Link: https://lore.kernel.org/r/20220808141246.5749-5-povik+lin@cutebit.org
Signed-off-by: Mark Brown <broonie@kernel.org>